It might not be your lifestyle it could be a B12 deficiency. B12 is essential for energy, mood, and overall wellness and when levels are low, your body feels it. Our Low B12 levels can lead to fatigue, numbness, irritability, and moreyet many people don't realize they're deficient. The good news? Testing and treatment are simple with options like injections or dissolvable tablets. When Do You Feel Less Tired After B12 Shot? I receive monthly intramuscular vitamin B12 (cobalamin) injections, but my serum B12 level measured two weeks after the injection is only 268 pg mL; why is it low and how should the dosing Feeling more tired, sluggish or low in mood? You're not alone shorter days and colder weather can leave your body needing that little bit of extra support. Vitamin B12 injections are